The History of Middle-earth is a 12-volume series of books published between 1983 and 1996 that collect and analyse material relating to the fiction of J. R. R. Tolkien, compiled and edited by his son, Christopher Tolkien. The series shows the development over time of Tolkien's conception of Middle-Earth as a fictional place with its own peoples, languages, and history, from his earliest notions of a "mythology for England" through to the development of the stories that make up The Silmarillion and The Lord of the Rings. It is not a "history of Middle-Earth" in the sense of being a chronicle of events in Middle-Earth written from an in-universe perspective. In 2000–01, the twelve volumes were republished in three limited edition omnibus volumes. Non-deluxe editions of the three volumes were published in 2002.
Some of the content consists of earlier versions of already published works, while other portions are new material. These books are extremely detailed, often analysing a scrap of paper to provide the full evolution of two or even three different versions of a passage that were rewritten over each other. Despite the great amount of material in the twelve volumes, numerous unpublished texts are still known to exist in the Bodleian and Marquette University libraries and in other papers held by individuals or organizations, such as the Elvish Linguistic Fellowship.
The first five books track the early history of The Silmarillion and related texts. Books six to nine discuss the development of The Lord of the Rings; book nine also discusses the Númenor story in the form of The Notion Club Papers. Books ten and eleven return to The Silmarillion material, including the Annals of Beleriand and Annals of Aman. Book twelve discusses the development of the Appendices to The Lord of the Rings and assorted writings from the last years of Tolkien's life.
- The Book of Lost Tales 1 (1983)
- The Book of Lost Tales 2 (1984)
- The Lays of Beleriand (1985)
- The Shaping of Middle-earth (1986)
- The Lost Road and Other Writings (1987)
- The Return of the Shadow (The History of The Lord of the Rings v.1) (1988)
- The Treason of Isengard (The History of The Lord of the Rings v.2) (1989)
- The War of the Ring (The History of The Lord of the Rings v.3) (1990)
- Sauron Defeated (includes The History of The Lord of the Rings v.4) (1992)
- Morgoth's Ring (The Later Silmarillion v.1) (1993)
- The War of the Jewels (The Later Silmarillion v.2) (1994)
- The Peoples of Middle-earth (1996)
A combined index was published six years after the series was completed as The History of Middle-earth: Index (2002).
A shorter version of volume 9 omitting material not related to The Lord of the Rings was published as The End of the Third Age.